1. Field of the Invention
The invention relates to a process for the production of 4-substituted acetoacetic acid derivatives from the corresponding acetoacetic acid derivatives.
2. Prior Art
It is known that in the case of the alkylation of acetoacetic esters, the alkylation takes place on the second carbon atom. Whenever the alkylation, however, is to take place on the fourth carbon atom, either the so-called dianion (discarbanion) of the acetoacetic ester must be formed. [J. Org. Chem., 29, (1964), p. 3249; J. Am. Chem. Sec., 92, (1970), p. 6702; J. Am. Chem. Soc., 96, (1974), p. 1032], or else one must start out from the lithium salt of the corresponding 3-pyrrolidone derivative of the acetoacetic acid ester [Japanese Patent Publication No. 31,608 (1974)].
Whenever the dianion is formed with the aid of potassium amide in liquid ammonia, poor yields of dianion are obtained and thus also poor yields (less than 37 percent) of the desired 4-substituted product are obtained [J. Org. Chem., 29, (1964), p. 3249]. Only whenever the dianion is produced in two steps, namely, by first forming the monoanion by means of sodium or potassium hydride and by then converting the latter with n-butyl lithium into the dianion, are improved yields achieved. The yields even in such case are no higher than somewhat above 80 percent. Beside the desired 4-substituted products, 2-substituted products are also obtained which can be separated only with difficulty.
Whenever acetoacetic acid derivatives are alkylated according to the process of Japanese Patent Publication No. 31,608, first of all the lithium salt must be produced by means of expensive butyl lithium. In that case yields result which lie in the order of magnitude of those which are achieved when working with the dianion.